T-SQL unfinished transaction lock

Question

I tried to run the following query

BEGIN TRANSACTION t1
SET IDENTITY_INSERT existingTableA On
insert INTO existingTableA (columnsFromTableA)
SELECT (columnsFromIdenticalTableB) from column identicalTableB

problem is that I didn't commit the transaction explicitly and it appears that I cannot do it any more and it's still ongoing. the select operation from tableA never ends because of the lock I cannot kill ("Distributed transaction with UOW {2B9A3B1B-F3EF-4C5A-9AD8-F434EF9EA3EC} is in prepared state. Only Microsoft Distributed Transaction Coordinator can resolve this transaction. KILL command failed.")

how do I end that transaction?

Answer 1

Run DBCC OPENTRAN.

Then kill the open Transaction with KILL xx, where xx is the SPID.